Presence of functionally active beta-adrenoceptors in rat mast cells. Correlation between (--)[3H]-dihydroalprenolol binding and inhibition of histamine release

Mast cells in the autonomic nervous system and potential role in disorders with dysautonomia and neuroinflammation

Mast cells (MC) are ubiquitous in the body, and they are critical for not only in allergic diseases but also in immunity and inflammation, including having potential involvement in the pathophysiology of dysautonomias and neuroinflammatory disorders. MC are located perivascularly close to nerve endings and sites such as the carotid bodies, heart, hypothalamus, the pineal gland, and the adrenal gland that would allow them not only to regulate but also to be affected by the autonomic nervous system (ANS). MC are stimulated not only by allergens but also many other triggers including some from the ANS that can affect MC release of neurosensitizing, proinflammatory, and vasoactive mediators. Hence, MC may be able to regulate homeostatic functions that seem to be dysfunctional in many conditions, such as postural orthostatic tachycardia syndrome, autism spectrum disorder, myalgic encephalomyelitis/chronic fatigue syndrome, and Long-COVID syndrome. The evidence indicates that there is a possible association between these conditions and diseases associated with MC activation. There is no effective treatment for any form of these conditions other than minimizing symptoms. Given the many ways MC could be activated and the numerous mediators released, it would be important to develop ways to inhibit stimulation of MC and the release of ANS-relevant mediators.

Skin and hair follicle innervation in experimental models: a guide for the exact and reproducible evaluation of neuronal plasticity

The remodelling of skin innervation is an instructive example of neuronal plasticity in the peripheral nervous system. Cutaneous innervation displays dramatic plasticity during morphogenesis, adult remodelling, skin diseases and after skin nerve lesions. To recognize even subtle changes or abnormalities of cutaneous innervation under different experimental conditions, it is critically important to use a quantitative approach. Here, we introduce a simple, fast and reproducible quantitative method based on immunofluorescence histochemistry for the exact quantification of peripheral nerve fibres. Computer-generated schematic representations of cutaneous innervation in defined skin compartments are presented with the aim of standardizing reports on gene and protein expression patterns. This guide should become a useful tool when screening new mouse mutants, disease models affecting innervation or mice treated with pharmaceuticals for discrete morphologic abnormalities of skin innervation in a highly reproducible and quantifiable manner. Moreover, this method can be easily transferred to other densely innervated peripheral organs.

Aging and sympathetic modulation of immune function in Fischer 344 rats: effects of chemical sympathectomy on primary antibody response

In aged Fischer 344 (F334) rats, sympathetic innervation of the spleen is markedly diminished compared with young rats. To determine if this diminished noradrenergic (NA) innervation maintains a functional connection with the immune system, 3- and 17-month-old male F344 rats were treated with the NA-selective neurotoxin, 6-hydroxydopamine (6-OHDA), to ablate peripheral NA nerve fibers. In sympathectomized rats immunized with keyhole limpet hemocyanin (KLH), a T-dependent protein antigen, anti-KLH IgM, IgG, IgG1, IgG2b antibody titers were increased in young and old rats 14 days after immunization compared to vehicle controls. Furthermore, the number of IgM and IgG anti-KLH antibody-secreting spleen cells was elevated 7 and 14 days post-immunization. These effects were prevented by pretreatment with desipramine, a catecholamine uptake blocker that blocks 6-OHDA uptake and subsequent sympathectomy. Chemical sympathectomy also increased KLH-induced proliferation in vitro by spleen cells from old, but not young animals. Isoproterenol (ISO), a beta-adrenergic receptor agonist, elicited a rise in cAMP in spleen cells from NA-intact young and old rats, but the increase was attenuated in spleen cells from old rats. These results demonstrate that, although NA innervation in the F344 rat spleen is diminished with age, sympathetic signaling of the immune system remains intact. Thus, the SNS can inhibit antibody produced in response to a protein antigen in both young and old F344 rats.

Role of beta 1- and beta 2-adrenoceptor subtypes in preconditioning against myocardial dysfunction after ischemia and reperfusion

Using an isolated nonworking rat heart model, this study investigated the role of beta-adrenergic preconditioning (beta-PC) to attenuate myocardial dysfunction after an ischemia/reperfusion injury. After a 20-min stabilization period, the noradrenaline depleted hearts were perfused for 5 min with isoproterenol (ISO) before 40-min global ischemia (I) followed by 30-min reperfusion (R). ISO 0.02 microM provided significant protection versus unconditioned in vivo reserpinized IR control, causing a decrease of creatine kinase (CK) release (mIU/min/g wet weight) on reperfusion in coronary effluent, a preservation of the mean coronary flow (MCF) and preservation of left ventricular function assessed by the rate-pressure product (RPP). These beneficial effects were similar to those of ischemic preconditioning (I-PC) in both nonreserpinized and reserpinized rats. Propranolol (1 microM) and atenolol (10 microM) completely suppressed the ISO preconditioning. In contrast, ICI 118551 (2 microM) a highly selective beta -blocker, did not blunt the salutary effects of ISO on CK release and MCF preservation. These results indicate that ISO pretreatment provides a significant cardioprotection against prolonged ischemic myocardial injury. Although endogenous catecholamines are not necessary for I-PC in isolated rat hearts, cardioprotection provided by beta-adrenergic stimulation is quite similar to I-PC. This significant cardioprotection is mediated less by beta -adrenoceptor than by beta -adrenoceptor activation, which seems to play a crucial role in the beta-PC mechanism.

Influence of salmeterol and benzalkonium chloride on G-protein-mediated exocytotic responses of rat peritoneal mast cells

The long-acting beta(2)-adrenoceptor agonist salmeterol and the invert soap benzalkonium chloride share physicochemically important structures, namely a polar head group and a long aliphatic chain. Low concentrations of benzalkonium chloride have been shown to inhibit exocytotic responses in rat peritoneal mast cells by selectively interacting with heterotrimeric G-proteins of the G(i)-type. The present study investigates whether salmeterol inhibits, independently of beta-adrenoceptors, exocytotic responses of rat peritoneal mast cells induced by the direct agonists at G-proteins mastoparan or guanosine 5'-O-(3-thiotriphosphate) (++GTP gamma S++). Exocytosis was studied by secretion assays ([3H]5-hydroxytryptamine ([3H]5-HT)-release) using intact, streptolysin O-permeabilised or metabolically inhibited (antimycin, deoxyglucose) rat peritoneal mast cells. Both amphiphilics, salmeterol, and benzalkonium chloride, dose-dependently exerted biphasic effects on mastoparan-induced [3H]5-HT release in intact mast cells. In contrast to benzalkonium chloride, the dose-response curves for secretostatic and celltoxic effects of salmeterol markedly overlapped. Similar to benzalkonium chloride, salmeterol in non-cytotoxic concentrations (1-25 microg/ml) dose-dependently inhibited exocytosis induced by mastoparan (intact cells) or ++GTP gamma S (permeabilised cells). These findings indicate a direct, adrenoceptor-independent affection of G proteins by salmeterol in mast cells.

Hair cycle-dependent changes in adrenergic skin innervation, and hair growth modulation by adrenergic drugs

Skin nerves may exert "trophic" functions during hair follicle development, growth, and/or cycling. Here, we demonstrate hair cycle-related plasticity in the sympathetic innervation of skin and hair follicle in C57BL/6 mice. Compared with telogen skin, the number of nerve fibers containing norepinephrine or immunoreactive for tyrosine hydroxylase increased during the early growth phase of the hair cycle (anagen) in dermis and subcutis. The number of these fibers declined again during late anagen. beta2-adrenoreceptor-positive keratinocytes were transiently detectable in the noncycling hair follicle epithelium, especially in the isthmus and bulge region, but only during early anagen. In early anagen skin organ culture, the beta2-adrenoreceptor agonist isoproterenol promoted hair cycle progression from anagen III to anagen IV. The observed hair cycle-dependent changes in adrenergic skin innervation on the one hand, and hair growth modulation by isoproterenol, accompanied by changes in beta2-adrenoreceptor expression of selected regions of the hair follicle epithelium on the other, further support the concept that bi-directional interactions between the hair follicle and its innervation play a part in hair growth control. This invites one to systematically explore the neuropharmacologic manipulation of follicular neuroepithelial interactions as a novel therapeutic strategy for managing hair growth disorders.

Adrenergic activity on rat pleural and peritoneal mast cells. Loss of beta-receptors during the purification procedure

Adrenergic agonists inhibit the release of histamine from rat pleural and peritoneal mast cells stimulated with compound 48/80 to a degree dependent on their beta-activity. Isoprenaline takes part in a stereoselective inhibitory action in the range 10(-7)-10(-4) M. Adrenaline induces a similar response pattern, with inhibition at higher concentrations. The response profile, but not the maximum values of inhibition, is clearly dependent on the concentration of the histamine releaser. Noradrenaline by itself is a histamine releaser, no stereoselectivity being observed. In the presence of compound 48/80 it takes part in a non-stereoselective inhibitory reaction at low concentrations. Inhibition of histamine release by isoprenaline was antagonized by 10 or 100 microM propranolol except at the highest isoprenaline concentration (1 mM). Both atenolol and propranolol nullified the inhibitory activity of noradrenaline, but not the increased histamine release it induces at higher concentrations (at least when acting in conjunction with compound 48/80). When rat mast cells are purified through Percoll, a change in their response profiles is observed. Isoprenaline and adrenaline by themselves elicit non-specific release of histamine; with compound 48/80, release is additive in the case of isoprenaline and supra-additive in the case of adrenaline. Results point to the loss of beta-adrenergic inhibitory activity after purification.

Adrenergic agonists do not compete with the antagonist (-)3-[125I]iodocyanopindolol for binding to rat pleural or peritoneal mast cell adrenergic receptor

(-)3-[125I]iodocyanopindolol (ICYP), a high selective, high specific beta antagonist is employed to characterize beta-adrenoceptors on rat pleural and peritoneal mast cell populations. Results show that non specific binding is low, and that pleural mast cells exhibit greater number of receptors per cell (140,000) than peritoneal cells (90,000). Dissociation constants (Kd) are 0.37 +/- 0.01 and 0.55 +/- 0.02 nM for pleural and peritoneal cells, respectively. Competition experiments show that isoproterenol do not displaces ICYP neither in pleural nor in peritoneal cells. Low concentrations of propranolol displace ICYP from its binding sites, but atenolol does not. Results point to the existence in mast cells of mainly atypical. beta 2-receptors, since the agonist isoproterenol does not compete with the antagonist ICYP.

Autacoid and beta-adrenergic agonist modulation of N-formylmethionyl-leucyl-phenylalanine evoked lysosomal enzyme release from human neutrophils

Isoprenaline, histamine and PGE1 inhibit N-formylmethionyl-leucyl-phenylalanine evoked lysosomal enzyme release from human neutrophils. Their effects are dose-dependent and potentiated by 3-isobutyl-1-methylxanthine pretreatment of the cells. The order of activity is PGE1 greater than isoprenaline greater than histamine. The maximum of inhibition afforded by each agonist depends on the amount of the secretory stimulus, since it is higher at lower concentrations of the secretagogue. Isoprenaline effects are competitively antagonized by propranolol and are mimicked by fenoterol and salbutamol. These results suggest that human neutrophil functions are modulated by endogenous control mechanisms, that can also be activated by drugs acting on the same receptors as the endogenous mediators.

Mast cell receptors controlling histamine release: influences on the mode of action of drugs used in the treatment of adverse drug reactions

In drug-induced allergic diseases of the immediate type (anaphylactic and anaphylactoid reactions), the primary target cells are tissue mast cells, which discharge their granular content upon interaction with different secretagogues (immunological releasers; histamine liberators) on specific plasma membrane receptors. Experiments are reviewed here which report that IgE-mediated histamine release from mast cells, and the secretion of histamine induced by non-immunological secretagogues (dextran; compound 48/80; acetylcholine) are blocked by beta-adrenoceptor and H2-receptor agonists, their inhibiting effect being surmountable by beta-adrenoceptor blocking drugs and by anti-H2-antihistamines. Specific radioligands ([3H]-dihydroalprenolol; [3H]-cimetidine) binding to rat mast cell membranes points to the possibility that inhibition of histamine release is brought about by the activation of mast cell beta-adrenoceptors and H2-receptors. Drugs used in therapy of anaphylactic or anaphylactoid reactions may act either on tissue receptors, competing with released mediators, or by inhibiting the release of allergic mediators from mast cells, on activation of specific receptors located in mast cell plasma membranes.